The fastigial nucleus (FN) of the cerebellum will be studied with chronically instrumented dogs in the context of overstimulation and ablation in an effort to clarify its physiological significance. The FN causes a sustained hypertension during stimulation, as well as elevated left ventricular pressure, dLVP/dt maximal (myocardial contractility), left circumflex coronary artery flow and a transient tachycardia. To verify the suspected role of this nucleus during exercise, dogs will be instrumented to measure the above variables and chronically implanted with brain electrodes. Submaximal exercise will be performed on a treadmill before and after lesions in these nuclei. Secondly, the long-term effects of daily (24-hour) trains of stimuli to the nucleus will be performed in order to try and establish a permanent hypertension. The same parameters will be observed for up to 3 weeks of chronic stimulation. Post-mortem anatomical studies will verify the precise location of the brain stimulating electrodes and verify any remarkable vascular or cardiac pathologies associated with sustained elevated arterial pressure from FN stimulation.